I think it's time to change the default encoding to UTF-8.

There some modules already use UTF-8 as the default encoding.

# Json convert
org.springframework.http.converter.json.AbstractJsonHttpMessageConverter#DEFAULT_CHARSET

# From this MediaType think UTF-8 is already the default encoding
org.springframework.http.MediaType#APPLICATION_JSON_UTF8_VALUE
org.springframework.http.MediaType#APPLICATION_JSON_UTF8

Comment From: pivotal-cla

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Comment From: pivotal-cla

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Comment From: bclozel

@chenyhd Isn't ISO-8859-1 still the default encoding in the Servlet spec? Wouldn't this change break lots of applications as a result?

Comment From: chenyhd

Hi @bclozel, good point.

I was using version 5.0.4 and faced the same issue as #25328, fixed in 5.2.x

Other things spring web: 1. Use UTF-8 as the default encoding for 'text/plain'.and declarative, you will get 'text/plain;charset=UTF-8' 

org.springframework.http.converter.FormHttpMessageConverter#DEFAULT_CHARSET
org.springframework.http.converter.FormHttpMessageConverter#FormHttpMessageConverter
org.springframework.http.converter.FormHttpMessageConverter#applyDefaultCharset
  1. Use UTF-8 as the default encoding for 'application/json', but not declarative,you will get 'application/json' 
org.springframework.http.converter.json.MappingJackson2HttpMessageConverter

Should I continue? or close PR?

Comment From: chenyhd

org.springframework.http.MediaType#APPLICATION_JSON_UTF8 marked as @Deprecated and explain major browser use UTF-8 not servlet change to 'UTF-8' as default encoding

Comment From: chenyhd

I checked out more information, org.springframework.http.MediaType#APPLICATION_JSON_UTF8 marked as @Deprecated because of RFC 8259 Charset Encoding, But this only for application/json, I didn't found RFC for text/plain charset encoding.

Anyway - application/json from RFC - text/plain from Servlet

The current code is already compatible with both cases.

Comment From: bclozel

Looking at the current situation with form data, plain text and JSON, I think we're in the right place. The Jakarta Servlet spec version 6.0 stills states the following:

If the servlet does not specify a character encoding before the getWriter method of the ServletResponse interface is called or the response is committed, the default ISO-8859-1 is used.

I'm declining this PR as a result. Thanks for looking into it!